Low power radio frequency (RF) transceivers are becoming increasingly important for a variety of wireless communication networks including wireless metering, home automation, wireless alarms and sensor networks.
One feature of such systems is a low bandwidth requirement for the various wireless sensors and transducers nodes on the network. For example, RF receive channels operating in these systems can desire narrowband operation ranging anywhere from, for example, 5 kHz to 50 kHz while maintaining high performance sensitivity, adjacent channel rejection and low active power specifications.
A common type of receiver employed in these systems comprises an intermediate frequency (IF) receiver and these typically include an analog to digital converter (ADC) within the receive path.
The term “noise transfer function” (NTF) can be used for the transfer function of the quantization noise of the ADC. If the NTF has a notch in the transfer function, then the quantization noise of the ADC will experience attenuation at the ADC output in the region around the notch frequency, with maximum attenuation occurring at the notch frequency itself.
It is known that placing the NTF notch at IF increases Signal to Quantization Noise Ratio (SQNR) without the need to increase for example, ADC oversampling ratio, sampling clock frequency or modulator order. Accurately locating the NTF notch at IF, in particular in Continuous-Time Sigma-Delta (CT-ΔΣ) ADCs, is subject to manufacturing and temperature variations, and hence a method to autonomously calibrate is desired.